Metal matrix composites (MMC's) have long been recognized as promising materials due to their combination of high strength and stiffness combined with low weight. MMC's typically include a metal matrix reinforced with fibers. In selection of the fiber, it is widely acknowledged that one desires reinforcement fibers possessing high strength, a high elastic modulus, and a low coefficient of thermal expansion.
The use of metal matrix composites in the form of wires as a reinforcing member in bare overhead power transmission cables is of particular interest. The need for new materials in such cables is driven by the need to increase the power transfer capacity of existing transmission infrastructure due to load growth and changes in power flow due to deregulation. Desired performance requirements for such new materials include corrosion resistance, environmental endurance (e.g., UV and moisture), retention of strength at elevated temperatures, and creep resistance.
Important properties for performance are elastic modulus, density, coefficient of thermal expansion, conductivity, and strength. These properties are typically governed by the choice and purity of constituents (i.e., material of the metal matrix and fiber content) in combination with the fiber volume fraction. Of these properties, emphasis has been placed on the development of wires made from fibers with high tensile strength and stiffness. The focus on producing materials of high strength is driven in part by the assumption that in order for the composite to compete economically with conventional materials such as steel, its strength should be as high as possible. For example, in Ozawa et al., “Mechanical Properties of Composite Conductors using SiC Fiber Resinforced Aluminum Composite Wires,” The Electricity Society National Symposium, 1996, which discloses an aluminum wire reinforced with high strength fiber marketed under the trade designation “NICALON,” the need for MMC wires of “high strength” for use in overhead power transmission cables is described.
There is still a need for composite materials that have suitable properties for use in a wide variety of cables, particularly overhead power transmission cables.